Piston construction



May 19, 1931.

A. A. STEPHENS PI STON CONSTRUCTION Original Filed April 14, 192

Patented May 19, 1931 UNITED STATES PATENT OFFICE,

ARNOLD A. STEPHENS, OF DAVENPORT, IOWA, ASSTGNOR F ONE-HALF T0 GEORGE E.

' WEEKS, DAVENPORT, IOWA PISTON CONSTRUCTION Application filed April 14, 1926, Serial No. 101,949. Renewed April 9, 1931.

tor in determining the mechanical efiiciencyof internal combustion enginesis the design and construction of the piston. Some of the problems involved in piston design and construction, are friction; cylinder wall wear;

oscillation of the piston in the cylinder,

known as piston slap; ring groove wear, resulting in loss of compression and other evils; light weight; 011 control; heat conductivity, and piston distortion due to heat or wear. This invention contributes in many ways to the solutions of all of these problems.

Because of the relatively high coeflicient of expansion of aluminum and other light metals or alloys desirable for use in pistons, it has in the past been found necessary to provide a large clearance to insure against damage brought about by seizing. The aluminum pistons used heretofore have been characterized by this large clearance. Some of the well known results have been piston slap,

' excess ring groove wear, undue wear of cylinder walls, distortion of pistons and cylinder Walls resulting from uneven wear, poor oil control, noisy and generally inefiicient operatlon.

The primary object of my invention is to obviate these difliculties in aluminum pistons or in a piston of any other light metal or alloy.

Another object is to design a piston which is constructed of a light metal and so designed that the maximum strength is secured with minimum material.

A further object is to provide a piston which will not seize or score cylinders under unusual heat conditions.

I accomplish these and other important objccts by providing an aluminum piston of improved design adapted to be fitted with replaceable sections of cast iron or other material having a low coefiicient of expansion and so arranged as to mutually cooperate as hereinafter described.

In the accompanying drawings forming a part of the specification:

Figure 1 is an elevation view showing the improved piston mounted in a cylinder;

Fig. 2 is a sectional view on the line 2-2 of Figure 1;

Fig. 3 is a view similar to Figure 2 taken on the line 33 of Figure 1.

Fig. 4 is a fragmentary view illustrating the ring joint and locking member; and

Fig. 5 is a fragmentary sectional plan view similar to Fig. 2, but showing a separate and detachable block member behind the ring.

I have shown in Figure 1, a cylinder 1 of an internal combustion motor in which is mounted a piston 2 adapted to be recipro- Y cated therein through the. medium of a connecting rod 3 journaled on a wrist pin 4. The connecting rod is mountedon the main shaft in the customary manner. The piston, which is constructed of aluminum or aluminum al- 10y, has integrall formed therewith wrist pin bearing 4. sshown in Fig. 2, these may be formed with longitudinal ribs to reinforce the bearings and thus provide a rugged wrist pin support.

The piston comprises a head portion 5 and a skirt ortion 6. Within the head portion, in suitable grooves, are mounted a plurality of piston rings 7. These, as is well known in the art, function to maintain a compres sion in the cylinder head and to prevent the passage of burning gases past the head to the piston skirt. I prefer, for considerations to appear more fully hereinafter, to use four of these rings.

The skirt section of the piston is formed with a plurality of annular grooves 8 of greater width than those in the piston head. Within these grooves are placed hexagonal springs. As shown in Fig. 2, the springs do not completely encircle the grooves but extend about three-fourths of the circumference. The remaining portion of each of the grooves is fitted with a filler block 10, which may be formed either integrally with the.

pendicular channeled grooves and, as shown grooves of each end are aligned with respect to each other. WVithin these channels there is adapted to seat a locking member 12, comprising a single horizontal bar and two vertical bars. It will be observed, upon reference to Fig. 4, that the ends of the bands may approach and recede from each other. The movement of the ends of the bands in one direction is determined when these ends abut each other, and in the other direction when" the horizontal bars of the member 12 abut the faces of the cooperating grooves of the rings.

As intimated hereinbefore, the piston body is of special design. Vhereas the head portion 5 is truly cylindrical, the skirt portion 6 is, in effect, composed of a plurality of cylinders, that is to say the skirt portion comprises sections of cylinders of unequal radii. This structure is clearly depicted in Fig. 3, wherein the segment 13, which is substantially quadrantal, projects beyond the prolongation of the circumference of the skirt proper. It will be noted that this extended segment is positioned at the thrust side of the cylinder.

This structure may be obtained in any desired manner. One satisfactory method is to initially form the entire skirt portion with a radius equal to that of the segment 13 and then cut down the remaining circumference, leaving segment 13 as a protuberance, as shown in Fig. 3.

When the device is to be assembled for installation, the filler block and spring are placed in the groove in such a manner that the block, which is of the same circumferential length as the thrust segment, is positioned on the thrust side of the piston. The carrier band is forced down over the side of the piston and into the groove. This is then compressed by any suitable tool and the looking member 12 inserted in the cooperating grooves of the ring. The thrust segment of the piston skirt will be flush with the carrier band.

. Since the bands are contractable the assembled piston may be placed in the cylinder body fiush or with much less clearance than is customarily allowed to eliminate the danger of seizing or scoring when the motor is warmed up. After the band, set flush, has been run in, a small clearance will be pro vided due to the running in process, which will insure an efiicient operation of the piston.

A small amount of clearance has many advantages. It reduces the possibility of piston slap to a minimum. Better oil control can be secured where there is less clearance.

A small amount of clearance insures an even wear of a piston and cyllnder wall. Where small clearance is allowed, an engine can be run for a longer period without overhauling to replace pistons which have become distorted or which have become worn. It might also be noted here that the only portion of the piston on which there is any wear is the thrust segment. This segment will not wear in a way which will require replacement of a piston after use. The bands can be replaced at will for securing any desired clearance. It will thus be seen that overhauling costs will be substantially reduced.

It will now be appreciated that on the thrust stroke of the piston the whole thrust side i. e., the thrustsegment and the carrier bands is utilized as a bearing surface, while on the compression stroke the carrier bands form the bearing surface. Since the thrust side is the only portion of the piston body which comes in contact with the cylinder wall, any distortion of the body of the piston caused by heat will not effect its operation. On the thrust stroke, the thrust segment provides the same amount of oil surface as is secured by the usual piston construction. The heat of friction is thus reduced to a minimum, since there is not friction sufiicient to produce appreciable heat on the other side. y

In prior construction in which aluminum pistons were used there existed an outstanding objectionable feature. Owing to the high rate of expansion of aluminum, a large clearance had to be allowed. It is to be particularly noted that while the piston of the present construction is made of aluminum, the problem of clearance is really that of a cast iron piston. The bands with the lock to prevent outward movement beyond a certain limit determine the amount of clearance of the piston in the cylinder bore.

The carrier bands are maintained in expanded position by a strong spring. It will be noted that the band is in effect forced away from the thrust segment, since the spring acts with a substantial radial thrust on the band. The band is maintained in circular form by the cooperative action of the spring and filler block and hence the dangers from distortion, inherent in prior aluminum pistons, are obviated. The skirt portion of the piston on heating in effect spreads out from the thrust segment as a fixed point. Inasmuch as the remaining skirt portion is of reduced circumference, it will not contact with the cylinder bore even at very high jacket temperatures. This I conceive to be a material advantage inasmuch as it allows safe operation at higher temperatures at which the mechanical efficiency is greater.

With reference to the oil control. it may be noted that the lower edge of the skirt of the ordinary piston forms a single wipe edge. With this piston, the carrier bands formed two wipe edges tending to wipe the oil downwardly into the crank case. Since the bands protrude beyond the wall of the piston, except at the thrust segment, there is a space or recess between the bands where the oil may accumulatein the event that it works up above the lower band. Oil holes may be provided in the skirt which allow such accumulated oil to bleed down again. I conceive that in thus securing better oil control an additional material advantage is obtained.

It will be seen that I have provided a carrier band above and below the wrist pin' bearing. These carrier bands determine the amount of clearance of the iston and make it possible to secure a muc smaller clear ance than that obtainable in ordinary pistons. It will be appreciated that the bandsconjointly serve to prevent oscillation of the piston body about the wrist pin. Such tilting movement of the pistons causes sliding of the piston rings in their grooves and thus induces wear. This type of wear of the piston ring grooves is a prolific source of trouble because it eventually allows the passage of burning gases past the rings, makes oil control less efficient and reduces compression, with consequent loss of power.

It is believed that the advantages of this construction will now be appreciated. The desirable features of the iron and aluminum pistons have been combined in one. The pis ton is composed of a light metal. The decrease in weight is accomplished without in any manner impairing the strength of the piston body. The construction insures a piston which will not score the bore of the cylinder or produce uneven wear thereon. The piston additionally insures silent running at all jacket temperatures.

IVhile I have shown and described a practical embodiment of my invention, it is to be understood that this is merely for'purpose's of exemplification, for since the essential fea tures may be incorporated in other specific mechanical constructions, I do not wish to be restricted to the particular device shown, except insofar as such restrictions are imposed by the sub-joined claims. v

I claim:

1. A piston comprising a head portion and a skirt portion, carrier bands mounted in the skirt portion, said bands being flush with the skirt portion on the thrust side of the piston but protruding beyond the skirt for theremainder of said skirt and means to limit the expansion of the bands.

2. A piston provided with a head and skirt, annular carrier bands mounted in the skirt above and below thewrist pin axis and means to maintain said bands radially immovable withrespect to the piston on the thrust side and flush with the skirt portion at the said side. 1

3. In a piston, means to maintain the thrust side thereof in continual engagement with the cylinder wall substantially throughout the thrust stroke comprising an annular substantially continuous spring pressed member flush with the piston at the thrust side but protruding beyond the piston wall at the remaining portions thereof. 4. A piston comprising a cylinder portion, a skirt portion having aradially extended segment adapted to contact with thecylinder bore, a carrier band resiliently mounted in the piston for a portion of its circumference butinflexibly mounted in the piston at the said extended segment.

5. A piston comprising an eccentric head portion, a skirt section adapted to contact with the cylinder wall at the. thrust side only head and an annular carrier band mounted in the I skirt section adapted to contact with the cylinder wall throughout its operative surface.

6. An aluminum piston comprising a circular head and non-circular skirt portion, wrist pin bearings formed in the skirt portion, sub-- stantially continuous carrier bands of a different material mounted.on' each side of the bearings, the exterior periphery of the bands being vertically aligned with one portion of the skirt but not with the remaining portion.

7. A piston comprising a head and skirt, the skirt being formed with an extended segment on the thrust side thereof, carrier bands extending around the piston and mounted in the skirt portion thereof, said bands being flush with the extended segment and protruding beyond the remaining skirt portion.

8. A piston comprising head and skirt portions, the skirt portion being formed of two segments of cylinders of unequal radii, a substantially continuous carrier band mounted in the skirt portion flush with the segment of greater radius.

9. A piston comprising head andskirt portions, the skirt portion being formed of segments of cylinders of unequal radii, annular grooves in the skirt portion, substantially continuous carrier bands mounted in the grooves flush with the segment of greatest radius.

10. A piston comprising a head and skirt portion, the head portion being annular and the skirt portion comprising sections of cylinders of unequal radii, annular grooves in the skirt'portion, continuous carrier bands substantially flush with the segment of great;

er radius.

12. A piston comprising a head portion provided with piston rings, a skirt portion comprising segments of concentric cylinders of unequal radii, annular grooves in the skirt portion, resilient elements mounted in ,the grooves conforming in circumferential extent to the segment of less radius, non-resilient elements also mounted in the grooves and conforming in circumferential extent to the segment of greater radius and carrier bands mounted in the grooves enclosing the said resilient and non-resilient elements.

13. A piston comprising a circumferential 'head portion and a circumferential offset skirt portion wrist pin bearings carried by the skirt portion, carrier bands of defined expansibility mounted above and below the,

wrist pin bearing, said bands being radially immovable at the offset skirt ortion.

14. A device of the class escribed, com

prising a piston having ahead and skirt, annular grooves in the head and piston-rings therein, annular grooves in the outer wall in rear of said ring sections, adapted to hold of said skirt, near the ends thereof, of relatlvely greater width than the first named grooves, expansible ring sections of relatively greater width than the piston rings held in said last named grooves, resilient elements the same yieldably in expanded position, and means for limiting the outward movement of said ring. sections.

15. Apiston. body comprising an aluminum head and skirt, bearing rings mounted in grooves in the skirt, the rings being spaced from the bottoms of their cooperating grooves, and -means carried by the skirt to l prevent yielding of a portion of the rings toward the groove bottoms. v

, 16. An aluminum piston comprising a head 7 portion provided with piston rings, a skirt portion formed witlrannular grooves in the outer-wall thereof and near the ends of said skirt, expansible ring sections of a dilferent material mounted in said grooves and provided with means-for limiting the expansion, resilient elements interposed between the rings and groove bottoms adapted to hold the rings. 'yieldably in expanded position whereby the piston skirt may expand or contract without affecting the circumference of the ring sections. A

17.- A piston comprising a head portion provided with piston rings, a skirt-portion formed with annular grooves in the outer wall pand or contract without affecting the circumference of the ring sections.

18. Apiston comprisingahead portion provided with piston rings, a skirt portion formed with annular grooves in the outer wall thereof and near the ends of said skirt, of relatively greater width than the piston ring grooves, expansible skirt sections separable from the skirt mounted in the grooves and provided with means for limiting the expansion thereof, resilient elements interposed between the rings and groove bottoms adapted to hold the rings yieldably in expanded po sition whereby the piston skirt may expand or contract independently of the sections.

- 19. A piston for internal combustion engines comprising a body having a head and skirtmade of a material having a higher rate of heat expansion in the engine cylinder, and

fitted in the engine cylinder with suflicient clearance to provido'for said difference in expansion, means having definite circumferential dimensions independent of its contact with the cylinder carried by said piston body having bearing engagement with the walls of the cylinder at all temperatures, and means interposed between the bearing face portion of said means and said piston body adapted to yield when the piston body expands to pro vide for the difference inv the rate of expansion of the piston and bearing means, and a rigid engagement between said piston and said means on the explosion thrust face of the piston.

20. A piston for an engine cylinder comprising a cylindrical head port-ion, a skirt portion having a radially extended segment on the explosion thrust side thereof adapted to contact with the cylinder of said engine,

a split carrier band resiliently mounted in the piston fora'portion of its circumference but rigidly mounted in the piston at the said extended segment substantially flush therewith, and means slidably interconnecting the ends of said carrier band to limit the diameter of the same.

21. In a piston for an engine cylinder, a bearing ringof greater diameter than the piston head positioned Within a groove in the body of said piston and having a portion thereof rigidly seated against the bottom of said groove adjacent to the thrust face of said piston body and flush with said thrust face, said pistonbody being thermally expansible independently of said bearing ring, and

means slidably engaging the ring for limiting the diameter of the same.

22. A piston for the cylinder of an internal combustion engine comprising a body provided with a head and skirt made of material having a higher coeflicient of expansionthan the engine cylinder, expansible bearing rings surrounding said piston body ongageable with the walls of said cylinder at all temperatures thereof, resilient means positioned between said bearing rings and body of said piston to expand said bearing rings into engagement with said cylinder walls and to permit expansion and contraction of said piston body independently of said bearing rings, and stop means cooperating with the ends of said bearing rings to limit the expansion thereof.

23. A piston for internal combustion engines comprising a body having a head and skirt made of material having a higher rate of heat expansion than the engine cylinder and fitted within said cylinder with suificient clearance to provide for said difference in expansion, bearing rings having definite circumferential dimensions independent of their contact with said cylinder carried by said piston body and being made of material having substantially the same rate of heat expansion as said cylinder in order to remain in contact therewith at all temperatures thereof, resilient members interposed between said piston body and bearing rings adapted to yield for allowing expansion and contraction of said piston body independently of said bearing rings, and rigid means interposed between portions of said piston body and bearing ring to provide a rigid engagement between said piston body and bearing rings on the explosion thrust face of said piston.

24. An aluminum piston comprising a head portion provided with piston rings, a

skirt portion having circumferential grooves therein, split expansible bearing rings of a different material mounted in the grooves, means to maintain the rings circular comprising a backing segment seated in the grooves, locking members carried by the rings and adapted to limit the expansion thereof, and circumferentially immovable means to retain the rings in expanded position.

25. In a piston, comprising a head and a skirt, a split bearing ring mounted in a circumferential groove in the skirt, and means to maintain the ring circular and of a circumference normally less than the cylinder bore comprising a backing plate mounted in the groove bottom at the thrust side of the piston and extendingan appreciable distance around said groove, a locking member for the ends of the ring, and a spring interposed between the ring and groove bottom adapted to hold the ring against the backin plate.

26. In combination with a cylin er, apiston having a head portion provided with the usual piston rings, a skirt portion provided with expansible bearing rings mounted in circumferential grooves in the skirt, and a backing segment carried by the bottom of the groove on the thrust side whereby the bearing ring is held radially immovable between sa1d segment and cylinder wall, and means carried by the ring to limit its expansion, whereby the bearing rings operate in the cylinder with clearance.

27 In combination with a cylinder, a piston comprising a head and skirt portion, an expansible bearing ring mounted concentrically with the piston in a groove in the skirt and adapted to operate in the cylinder with a clearance, and means for preventing movement of the ring with respect to the skirt on the thrust side of the piston comprising a segment carried by the bottom of the groove on the exterior arcuate surface of which the ring isadapted to bear, and means carried by the ring adjacent the plate adapted to limit its expansion.

28. An aluminum piston comprising a head portion provided with piston rings, a skirt portion having circumferential grooves therein, split expansible bearing rings of a different material mounted in the grooves, means to maintain the rings circular comprising a backing segment seated in the grooves, locking members carried by the rings and adapted to limit the expansion thereof, and means to retain the rings in expanded posi tion.

29. A piston comprising a head portion provided with piston rings, a skirt portion having circumferential grooves formed therein, backing members seated in the grooves on the thrust side of the skirt, expansible bearing rings mounted in the skirt portion and means carried by the rings to limit their expansion and coacting with said backing members to retain the rings in circular form.

In testimony whereofI aflix my signature.

ARNOLD A. STEPHENS. 

